1. Field of the Invention
The present invention relates to a digital radio telephone apparatus such as a digital cordless telephone apparatus or a digital portable telephone apparatus designed to perform bidirectional speech transmission via a radio channel according to a digital scheme and, more particularly, to a digital radio telephone apparatus having a recording/reproducing function.
2. Description of the Related Art
Recently, a PHP (Personal Handy Phone) system has been developed to be put into practice. In this system, bidirectional speech transmission between a base unit and each of portable units (portable hand set) via a radio channel is performed according to the digital scheme, and each portable unit can be used outdoors like an existing portable telephone apparatus when a digital cordless telephone apparatus of the PHP system is used indoors, both the base and portable units can be used to perform speech communication in the same manner as an existing cordless telephone apparatus. This apparatus is used outdoors in the following manner. For example, a large number of radio base stations (corresponding to radio base stations for portable telephone apparatuses) are installed in public telephone booths distributed in a town, and each station is connected to a public telephone line. With this arrangement, each radio station is regarded as the base unit of a cordless telephone so that speech communication can be performed by using a portable unit even in a place outside the home.
A recording/reproducing function provided to a conventional analog cordless telephone apparatus is expected to be added to the above digital cordless telephone apparatus. As is apparent, for example, a recording/reproducing function for performing a so-called simultaneous answering/recording operation is expected to be added to the digital cordless telephone apparatus. The simultaneous answering/recording operation is an operation of recording a speech signal generated by a caller, in performing an automatic answering/recording operation, simultaneously with reproduction of a response message from the user upon reception of an incoming call. First of all, in order to add the recording/reproducing function for such a simultaneous answering/recording operation to the above digital cordless telephone apparatus, the corresponding arrangement applied to an existing analog cordless telephone apparatus may be directly used. That is, a response message storing IC memory, a speech communication recording IC memory or a tape recorder, and a speech codec circuit for reading/writing speech data in/from the IC memory, which are used for the existing analog cordless telephone apparatus, may be incorporated in the digital cordless telephone apparatus.
If, however, a circuit for reproducing a response message to perform a simultaneous answering/recording operation, and a circuit for recording/reproducing a message from a caller are independently arranged in the apparatus, the circuit size is increased. As a result, problems are posed in terms of the size and cost of the apparatus.